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10th. It must free vessels from all necessity of pilotage, and, conseqnently, avoid their circulation among the islands, keys, and reets, which in the passes require the services of a pilot.
11th. It must also do away with the necessity of towing, at least as far as the river, where the wind often permits Vessels to ascend directly from the English Town as far as New Orleans.
12th. It must have a constant depth of 22 to 24 feet of water, in order to permit the access to the river of ships of the greatest tonnage.
13th. It must be forever secure, by its conditions of existence, from those perturbations which render the passes impracticable to the navigation of large vessels; that is to say, from the action of the sea, from accretions from the river, from sand-banks formed by any agency.
It will be seen from the description we are about giving of the proposed canal, and from its topographical conditions, that it will satisfy, strictly and precisely, all these exigencies.
Section 2.— Topographical and hydrographical description.
Wben, going down the Mississippi, we arrive at Fort St. Philip, we see the majestic course of the river developing itself on a length of eighteen miles, as far as the head of the passes, without sinuosities or turns. The mass of water nioves always in the same direction, without any sensible inflection in its banks. But as the current came from the southwest, and bas infected to the southeast from the bend of the forts, the result is that its greatest swiftness and depth are near the left bank, while the water is smoother and deposits its accretions near the right bank. From three to eight miles below the fort repeated soundings have given us depths of 24, 25, 26, aud 28 feet, at a distance of 20 and 25 feet from the bank; 20 feet farther the head sinks to 62, 71, and 87 feet.
If we stop seven miles below Fort St. Philip, that is to say, precisely on the 90° 31' longitude west, we are at a mean distance of twenty-seven miles from the passes, which, from the declivity assigued to the river, to wit, 34 inches per mile, would represent a difference of 74 feet in the level from that point to the surface of the Gulf. Levelings made by us between this point and the Gulf show that it is only 3 feet higher than the Gulf at mean tide. It is ther-fore possible to shorten the navigation of the river twentyseven miles at this point, having to make up for a ditforence of only 31 feet declivity at mean water, and 7 feet at the highest water-mark.
This point being chosen at the head of the canal fulfills completely the first three conditions mentioned above. Let us see if it can satisfy, equally, the others.
If from the top of one of the few huts to be found on that bank, upon which, from Fort St. Philip to the sea, there exists no important establishment except the salt-works opposite the Jump-if from this observatory we turn our back upon the river and we look around us, we will see, extending indefinitely to the horizou, a scene of extreme monotony. The left bank of the river from the fort to the head of the passes is a mere neck of land hemmed in between the waters of the Mississippi and those of the sea. Its width, except at few points, does not exceed a mile, and at other points it is narrowed down to a few arpents. An additional mile may be considered as a dependency of the main-land, althongh cut up in every direction by canals, lagoons, and bayous of an average depth of 2 or 3 feet during tide time, and which are transformed into mud or sand-banks during low tides. Beyond this is a series of small bays from 3 to 3 feet deep, and studded with a quantity of islets, between which the sea opens deeper pisses or deposits accretions upon which pumerous oyster-banks are formed.
On the right, on the east line, one of these islets, Bird's Island, of more importance than the others from its length, runs from north to south a distance of four miles; ou its eastern point a watch-tower has been built, which commands a view of the sea. Going up from east to north, a long sandy beach, known as Sand Island, forms the limit of these low lands.
In the direction of the northeast, the last of these islands, called the Pavillon Island, fronts an island situated six miles off at sea, and to which we will have occasion to refer; it is Breton Island.
To the left of this islet another neck of land, called the Hard Batture, runs out to meet au island, two and one-half miles long, Grandes Coquilles Island, which is in the due north point, and is only separated by a channel from the smaller Coquille Islands connected in low water with the main-land of Fort St. Pbilip.
It is, therefore, in this semicircle, the center of which we have placed on the river seven miles below Fort St. Philip, and the circumference of which runs from the southeast to the northwest, that a real archipelago of islands and of lands cut up by lagoons and bays, but uniform in their aspect and their nature, is comprised, evidently created by sea-deposits, but with materials furnished by the Mississippi; they reveal to a geological study the character of the marly accretions to be found in all the deposits of the river. The bottom of the bays and lagoons, covered at certain points by a soft mire which has not yet hardened, is everywhere else perfectly hard, and the purest clay
sticks to the lead. All these lands, scarcely out of the sea, and which it covers in its usual tides and destroys or tears up in its angry moods, only offer to the eye the monotonous vegetation of sea-weeds, gramineous plants, and mangroves.
The radius of this semicirele, from its center on the river to Pavillon Island, is of six miles. It is on this radius that the projected canal runs. It cuts first the two miles of solid land, crosses the large bay in that part of it where the water is lowest, crosses a prairie one mile wide, and, pursuing its course through lagoons and mud-banks, it reaches Pavillon Island, having its outlet in the pass of Breton Island.
It may appear singular that we should have chosen this point of the coast when we have already stated that three miles below the salt-works the neck of land has only a width of a few arpents between the river and the sea ; but a simple reflection will justify this apparent contradiction. The object in view is not simply to cut the canal to the sea, which may be done by cutting through a length of 1,000 feet, but it is to open it on the deep sea, that is, at a point where large ships drawing 22 to 24 feet can have easy
Outside of the main-land there is a border of batture, which in some places projects twelve or fifteen miles, and beyond this batture, whose conventional line is at a depth of 12 feet, the declivity is sometimes so small that a long distance must be made before the necessary depth of water can be met.
The distance of six miles which we have found for the line of the caval is the shortest between the river and the deep sea that can be formed from the forts to the passes, and it is even vecessary, in front of Pavillon Island, to dig and continue the canal through a batture for a distance of 3,000 feet to arrive at the required depth.
Another circumstance, altogether exceptional, militates in favor of this side. Hydraulic works or works of embankments made in 2 or 3 feet of water may be considered as made on land; wbile those made in 8 or 12 feet of water are extremely difficult and expensive. Now, on the line iudicated, about three-fourths of the passage are made on the land, and for the other fourth, the average depth of the sea does not exceed 2 feet. This plau combines, then, the advantages of the minimum of distance aud the minimum of cost.
Let us examine the access to the canal from the seaside :
We have already said that by following the northeast line, which is that of the canal, there would be found on the main sea, and at a distance of about six miles from Pavillon Íslaud, an island known as Breton Island. This island, which had formerly a length of six miles, and was then occupied by a colonist living with his family in the midst of the vast Gulf, was cut up by a sea-storm that took off from it an islet of half a mile in length, on which a watch-tower has been raised, which would be replaced by a light-house. As cut up as it is, this island, with the batture that extends on its right and left, has a length of ten miles, running almost straightly from east to west, and forining consequently an excellent shelter for vessels against north and northeast winds.
The coast of the river above the fort, and the large peninsula of Lake Borgne, afford protection against the northwest winds.
The coast of the river below the fort shields the canal from southeast winds. Finally, the south winds are intercepted by the large eastern opening of the delta.
The bead of the canal is therefore exposed to the east wind alone, and it is precisely this wind which will bring the vessels from the main sea; it can only facilitate their arrival and bring them in a clirect line to the port.
The direction of the canal being northeast, it will be seen that the ships with an east wind will sail directly for the canal with the wind over the quarter, a very favor: able direction indeeil, both for facility of maneuver and speed. The pier that terminates the canal opens in a semicircle, to afford ample and convenient room.
The existence of natural shelters being thus established, can we depend equally upon the depth of water in the channel formed between Pavillon and Breton Islands? It is principally that point which we have investigated.
Besides numerous soundings in all that region, represented graphically, we have inserted in the plans the series of soundings from the head of the canal to the watchtower on Breton Island. This line consists of the following points: 26 feet, 36, 35, 36, 39, 34, 19, 14, and 12. These last three soundings are in the vicinity of the batture of Breton Island, the former occupying a breadth of four miles. We have also (although it was one mile north of the canal, and consequently of no great importance) determined a second line from the most advanced point of the reef of Breton Island and of the island of the Hard Batture, where that pass is narrowest, and we have found the following figures: 21, 36, 32, 28, 32, 332, 36, 10. It will be seen that ships will bave certain access to the canal with fully suficient water.
But, with the contimual changes made by the Gulf in that region, is there no fear of the futrire creation of obstacles, such as those that obstruct the passes of the river ? We will reply to this query first by argnments, then by facts. It is very true that the tendency of the sea is evidently to fill up all its eastern portion along the river, ai d to fill up gradually all the lagoons so as to form them into main-land. If it destions accidentally, it creates constantly, and for this very reason certain passes must necessa
rily remain where the swiftness, and consequently the depth, will increase instead of diminishing. Such is the case with the two passes that exist west and east of Breton Island, that is, on one side between that island and the promontory caused by the canal, and on the other between that same island and the great batture which begius at Grand Gosier Island and serves without interruption as a basis to the archipelago of the Chandeleur Islands. It is by these two passes alone that communication can be obtained between the Gulf and the Mississippi Sound within one degree of longitude.
So much for arguments. As to the facts, the comparison of the soundings made in 1827, and consigned on the tine map of the Gulf of Mexico, by Mr. Edmund Blunt, with the soundings made by us, prove that the depth of water has increased in the west pass of Breton Island since that time. These first soundings give 36 feet only on one point of the coast; everywhere else they give 18 and 24 feet.
Among all the advantages we have pointed out in this predestined locality, there is one that we have mentionel too concisely, and which plays too important a part that we should not dwell upon it now. It is the nature of the sea-bottom and of the soil of the island which the canal will have to cross. Reiterated geological soundings that have uniformly given us 14 feet of sand-clay enabled us to verify that it is impossible to find a species of clay more firm, more homogeneous, and more resisting. The anchor bites freely, and once imbedded in it, rums no risk of dragging: The vessels are, therefore, certain of being able to lie at anchor outside of the canal as long as may be desired, under shelter of either Breton Island or Bird Island.
The precious quality of this soil will be again evident when we take up the question of construction.
These general conditions once determined, their consequences may be drawn naturally. The vessels arrive from the high sea into a sort of guif, opening due east, and circumscribed to the south by the northern bank of Pass à Loutre, to the west by the river and Birci Island, and to the north by Breton and Grand Gosier Islands. In this gulf cannot be found a rock, a reef, or an islet. Its depths rary in the mean line 90 to 36 feet. The light-house on Breton Island and that on the pier of the canal will point out the entrance to the latter. There will be, therefore, no necessity for pilots ; no port will ever have an easier and more direct acce88.
It is useless to add that, until their entrance in the canal, the ships will have no need of tows. Once in the canal, the towing will be performed by means of locomotives running on a railway built on the top of one of the levees. It is, therefore, only after their arrival in the river that the ships will, if the wind is not favorable, employ tow-boats to ascend the river.
Of all the conditions we have set forth as necessary to an artificial opening of the Mississippi, two yet remain to be fullilled, the creating of a depth of 22 to 24 feet, and the assurance that this depth cannot be altered or reduced by either the sea or the river.
These two conditions do not depend on topographical or hydrographical data, but on the construction of the canal itself.
Section 3.- Draught and construction. It may be asserted with confidence that no work more important in its consequences has ever presented fewer difficulties of execution, aad involved less cost, than the canal of which we have demonstrated the necessity. Consequently, its description need not be long nor complicated.
First, the difference iv declivity between its two extremes is of 41 feet ; the difference of level between the waters of the river and those of the sea is only of 3 feet, in ordinary conditions. When the river rises, the sea may be below the level of the river as much as six feet.
The slope of 41 feet on the horizontal line is almost entirely level from a distance of 3,000 feet from the river; it is therefore reclaimed by a single lock, and outside of this the canal may be considered as being perfectly level. But for the necessity of protectting the talus against the surf of the sea, there would be no necessity for another sluice at the other end.
It is an entirely level country, with no obstacles to overcome, no trenches to be made, no rivers to be crossed, no excavations to be made. Its alimentation presents no difticulties; no fears need be entertained of filtrations or leaks occurring, save those that mnight affect the solidity of the work. It is in truth a gigantic ditch, usheltered, perfectly rectilinear, and of complete uniformity on a length of six miles. It will be a great undertaking only by its olimensions and its results.
To determine these dimensions we must remember the object of the canal, wbich is to open a large road to sea-navigation, to ships and steamers of the greatest size ; to continue in some way the drauglit of the deep sea and of the river without sensible interruption.
But few examples of analogous works can be consulted by way of comparison, and
among them only one has been executed, another is now in course of execution; the two others are as yet but projects.
Jiles. Feet. Feet.
147 6 100
Feet. Feet. Feet. Feet. 20
40 172 23 2 63 300 21 23 32
47 210 3 80 400
We owe some explanations on the remarkable differences presented by the dimensions proposed by us compared with the others in the above table.
The prevailing thought in our mind has been to leave free scope to the creations of the future, and, while remaining within the limits of what is possible and reasonable, to give a wide margin to the already manifest tendency to constructing very large ships. Therefore, for all the dimensions claimed for their admission, we have gone beyond the given corresponding figures for tho other canals; 24 feet draught at low water; 400-feet locks; 80 feet of openings to the sluices. We have taken as a basis for these speculations on the future the dimensions of the largest steamer ever constructed except the Great Eastern. The Adriatic has a length of 345 feet and a width of 75 feet outside the wheels. She draws 23 feet of water, and measures 4,144 tons.
The Great Republic, the largest sailing-vessel existing, draws 23 feet and has a length of 302 feet and a breadth of 48 feet.
Some time will elapse before New Orleans can see vessels requiring such outlets arrive at her wharves; but, at all events, if such should come, she will be able to admit them. However, there is a figure for which we have remained far below the large sea-canals; it is that of the width of the canal. It is only 100 feet; that is ten feet less than the narrowest of these canals, the Caledonian Canal.
It must be known, first, that the Caledonian Canal, however small its sectiou, gives access to the largest merchant-ships and to steamships and propellers of a large tonnage. Moreover, in its length, which is of fifty-nine miles, comprising thirty-eight miles in Lakes Lochy, Oich, and Ness, there is much circulation in opposite directions. It is, then, necessary that two large ships should be able to pass each other. The same condition exists in all other canals mentioned.
Such is not the case with our Mississippi Canal, Circulation there can only take place in one direction, according to whether the towing locomotives are going from the river to the sea or from the sea to the river. By this combination there is a gain of one sluice, and for a long time to come circulation will not be rapid enough to require other means. Thus a convoy of ships arrives from sea and enters the neck formed by the two piers. The locomotive takes hold of it and tows it to the nearest or seawaril slnice, which opens, and the convoy enters the locks. The gates of the seaward sluice close; those of the head sluice open; the level is formed and the convoy enters the river. Then the vessels, awaiting at the wharf on the river, avail themselves of this leveling to enter in their turn into the canal, and they are towed to sea.
The result from this system of working is that the width of 100 feet in our canal is equivalent to a width of 200 feet in canals where ships meet and cross each other. Let us add here, moreover, that toward the center of the canal will be found a basin 600 feet long and 200 feet wide, to be used as a wet-dock.
It will be easily understood that this system would have been impossible had the canal bad a greater length. The time necessary for the towage would have occasioned too much delay to ships awaiting ingress or egress.
According to the table already quoted the movements of import and export nearly balance; there were, in 1858–59, 2,062 arrivals and 2,185 departures, and in 1859-'60, 2,052 arrivals and 2,235 departures.
In the month of November, when this movement was most animated, 267 vessels arrived, to wit, 152 ships, 40 barks, 18 brigs, 29 schooners, and 28 steamships. This gives an average of 9 per day, and as many departures. By doubling these figures the result would only be 18 ships in each direction, or a daily circulation of 36 ships, which, boy taking the average of 574 tons per ship, would give 20,664 tous.
The time necessary to cross the two sluices being about fifty minutes, it will take the locomotive one hour and ten minutes to take the vessels and run the six miles. This moderate speed has for object not to injure the embankment; each trip will then occupy two lours. At the rate of twelve trips per day it is three ships, or little over 1,700 tons per trip.
Nothing can be more practicable than these calculations, although they correspond to a circulation double of that which takes place at the time of the year when the commercial movemeut attains its maximum.
If we follow the plan of the canal in its short and simple line from the river to the sea, we will find at its head, on the Mississippi, a liglit-house placed on the upper embankment; the object of this light-house is to point out to ships coming down the point where they must stop. There is to be formed from this embankment, running to a length of half a mile, a wharf, along which the ships and tows they may need will line themselves. Behind the wharf, and at the head sluice, is placed the house of the keeper of the canal and the custom-house ottice; opposite, on the other side of the lock, is the building used as the locomotive-depot, and containing a machine shop and a storehouse for the urgent repairs and supplying of the vessels.
The head sluice, of a width of 80 feet, gives entrance into a lock 400 feet in length, closed by the middle sluice; the latter gives passage into a channel formed by levees in embankments. From this point the shape of the canal is uniform as far as the sluice at the sea-head.
This profile presents a section 100 feet wide at the low-water mark, 24 feet deep, and 30 feet wide at the bottom. The slope of the banks or talus is, therefore, on each side, of 35 feet base for 24 feet height; that is, about 11 to 1, corresponding to an angle of 32°. This easy slope is more than sufficient, with the compact nature of the soil, for the preservation of the bank.
On the right and left of the water-line a berme 15 feet wide is formed; it serves to receive the falling-in that might occur in the upper levee, and also to increase the strength of this levee and consolidate its base.
On each side of this base rises the levee formed with the earth from the canal. It is 10 feet high, and consequently meets the upper level of the lateral walls, the brickwork of which is 34 feet above the bottom of the canal. The width of the levee at its top is 15 feet, and for its greater solidity it will have sixty feet at its base; it is a slope of 49, corresponding to an angle of 20%.
On the lower levee (in relation to the river) the railroad for the towage of the ships is built. Two turning-tables, situated at the two extremities of the line, permit the direction of the locomotive to be changed.
From the middle sluice the canal runs a distance of 13,880 feet in main-land on a level. It is a prairie, cut in the last mile by a few unimportant lagoons. It crosses then the large bay on a width of 5,600 feet. It is during this passage that it spreads out in the basin that we have mentioned. This basin will be used as a wet-dock for the dredging-machines, for the boats employed in the service of the canal, and for the vessels which, for some reason, would need to stop on their way. Coming out of the bas the canal runs 4,000 feet through a prairie; it runs again into a series of lagoons of 3,000 feet, gains land once more for a distance of 2,600 feet, and finally crosses a last bay of 1,900 feet to arrive at Pavillon Island, wbich it cuts upon a length of 400 feet.
It is on the outer shore of this island—that which faces the sea—that the pile of masonry intended to contain the seaward sluice is constructed. There, also, will be the house of the keeper of the sluice.
The two arins of the lateral ernbankments of the sluice on the sea-side form the head of the double pier, which, starting from this island, run out in the deep sea in the direction of the axis of the canal for a distance of 3,000 feet, where the depth of 24 feet at low-water is found. These two piers, between which it will be necessary to excavate the batture, are the only works of art in the canal. And this work can only be looked upon as a feeble specimen of analogous works conceived or executed by modern science. Thus the dike at Cherbourg has 11,300 feet of length, in depths of 44 feet of water.
The pier of Plymouth has over 4,000 feet in 34 feet of water. The dike in the Bay of Delaware has 3,600 feet in a depth of 42 feet; that destined to form the port of Peluse, for the entrance to the Suez Canal, will have 18,000 feet of development until it attains a depth of 24 feet.
The south pier, on which the railroad will be built, will terminate at its end by a large mole of 100 feet diameter, in the center of which will be placed a light-house with lenticular apparatus.
The description gives a complete idea of the canal. We have now to show how the depth of 24 feet which we have given it cannot be subject to any change, either in increase or decrease.
The increase in the depth would have the inconvenience of undermining the foundations of the masonry or the base of the embankments and produce a caving in. This danger is not to be feared on the river-side. It will be seen that its waters scarcely penetrate in the canal; it could, therefore, only exist from the sea-side ; but, when the sea threatens, the onter lock is immediately closed and the whole channel is as smooth as a pond. As to the bottom of the lengthening of 3,000 feet situated between the two piers, its depth and its shelters are such that the sea will remain smooth thore at all
There remains the otherwise dreadful danger of a reduction in the depth ; that is, a